diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index 4032da8e21..b49ce536a6 100644
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -24,7 +24,9 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 #include <cerrno>
 #include <vector>
 #include <exception>